The availability of inexpensive microprocessors and sophisticated electronic components has facilitated implementation of advanced safety and convenience features in a variety of automotive and trucking applications. As control systems become more complex and sophisticated, they are capable of providing the vehicle operator with information having various degrees of criticality. Regardless of the type of information conveyed to the vehicle operator, it is important to consistently provide accurate information such that the vehicle operator may depend on the content of the information. Most operators would prefer to not have any information provided rather than having information of questionable reliability.
Recently, collision warning systems for vehicles have become commercially available. These systems utilize an electromagnetic beam, such as a microwave, laser, or ultrasonic beam, to detect the distance and/or closing rate between the host vehicle and a forward vehicle or other object to warn the driver of a possible impending collision. Obviously, it is important for these systems to consistently provide accurate information to the vehicle operator. Accurate information includes warning the vehicle operator when a collision is possible or probable, but also includes not warning the operator when a collision is unlikely or unprobable. That is, it is undesirable for the collision warning system to trigger false alarms since the vehicle operator may ignore it when an actual alarm condition is indicated or may disable the collision warning system altogether.
Some prior art systems automatically decelerate the vehicle to maintain a predetermined following distance behind a forward vehicle. An example of such a system is described in U.S. patent application Ser. No. 08/396,640 entitled "System and Method for Intelligent Cruise Control Using Standard Engine Control Modes", filed Mar. 1, 1995 and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated by reference in its entirety. Many prior art systems which provide a collision warning utilize a fixed distance threshold which may be measured in feet, or a headway distance which may be measured in seconds and varies with the current speed of the vehicle. However, such prior art systems do not account for the dynamic deceleration capabilities of the vehicle due to the current operating environment. Thus, these systems may unnecessarily trigger an alarm when the vehicle is capable of avoiding a collision without driver intervention.
Collision warning systems which trigger an alarm based on a fixed distance or fixed headway distance are particularly difficult to utilize in tractor semi-trailer vehicle applications due to the wide range of vehicle weights ranging from bob-tail to a fully loaded semi-trailer. In these applications the vehicle weight may vary by 300% or more. This results in a wide range of deceleration capabilities since a heavily loaded vehicle at zero throttle will decelerate less rapidly than a lightly loaded vehicle when descending a grade, and in many instances may even accelerate. Likewise, a heavily loaded vehicle can decelerate more rapidly when climbing a grade than a lightly loaded vehicle. Furthermore, medium and heavy-duty trucking applications experience more aerodynamic drag than typical automotive applications. Thus, dynamic determination of deceleration capability is particularly desirable for these applications which include MVMA Class 7 and Class 8 vehicles.